A modem (modulator-demodulator) or a device having a modem (collectively referred to as a “modem” hereinafter) is a part of a mobile communication device. Examples of the mobile communication device include mobile phones, data cards, and tablet computers.
A mobile communication device is capable of being served by a cell of a cellular communication network. When a cell is currently serving a mobile communication device, the cell is called a current serving cell of the mobile communication device. In an area where signals of the current serving cell (referred to as a “current cell” hereinafter) are weak and unstable (such area is called a “weak field” hereinafter), parameters such as signal strength and signal quality of the current cell may have little difference from those of neighboring, non-serving cells. When the modem is standby in the weak field, signal quality factor of the current cell is poor because signals are brief and unstable. When the signal quality factor of a neighboring cell, obtained by using an R algorithm, is better than the signal quality factor of the current cell, the modem performs a cell reselection operation to change the serving cell from the current cell to the neighboring cell. However, the signal quality factor of the neighboring call might also be poor. Due to the instability of signals in the weak field, the modem needs to perform cell reselection repeatedly, so as to ensure that the serving cell is a cell with an optimal signal quality factor. However, such repeated cell reselection increases standby power consumption, and reduces standby time of the modem.